Resonant tunneling diodes are nano-devices which have characteristics of negative differential resistance. They are widely used in digital and analog circuits to reduce components and decrease power consumption. In recent years, resonant tunneling diodes have been found to be an important choice for implementing terahertz device. GaN-based resonant tunneling diodes have inherited the advantages of III-nitride, such as high operating frequency, high power, high temperature resistance, etc, which has become a research hotspot. This paper introduces the basic situation of resonant tunneling diodes, reviews the progress of simulation and experiment, analyzes the influence of polarization field, and presents the challenges. The analysis provided in this paper may help the audience to become more familiar with current research efforts, as well as to provide inspiration for future III-nitride quantum device designs.